Interior Secretary James G. Watt yesterday sent Congress a bill designed to preserve the nation's dwindling wetland acreage, calling it the fulfillment of a pledge he had made as a mid-level Interior Department employe a decade ago.

As director of the Bureau of Outdoor Recreation in 1973, Watt said in a news conference, he outlined a comprehensive strategy to preserve wetlands, which are critical breeding areas for waterfowl and serve important functions in flood control and water purification.

"I called for it 10 years ago and nothing has been done," he said.

The bill, called the Protect Our Wetlands and Duck Resources Act, has been high on Watt's priority list since he took office. Watt said that draining already has destroyed more than half of the 215 million wetland acres that once existed in the 48 contiguous states.

"Every day we don't do something, we lose 1,000 to 1,500 acres," Watt said, calling for lobbying groups and "special interests" to help him secure the bill's passage.

But some environmentalists already have criticized the bill, saying it is riddled with loopholes and could thwart more comprehensive legislation by creating a false impression that wetlands are being protected.

The main feature of the bill is a provision that would forbid federal subsidies of activities that would result in the loss of wetlands, such as the construction of waste-water treatment systems or airports. But it would not stop federal water projects, military projects or oil and gas development.

"No genuine doubt exists that 90 percent or more of federal assistance is encompassed by these exceptions," said William Y. Brown, senior scientist at the Environmental Defense Fund.

Watt conceded that he did not know how much wetland acreage would be saved by the bill, but he said that was not important.

"The problem with government is paralysis by analysis," he said. "We'll figure these things out as we go along."